By Robert P. Adams, Philip Thomas and Keith Rushforth
Abstract: Abstract: A new conifer genus was recently discovered in northern Vietnam and named Xanthocyparis with two species: X. vietnamensis in Vietnam and X. nootkatensis (= Chamaecyparis nootkatensis) in western North America. This is the first analysis of the leaf essential oil of X. vietnamensis. The oil of X. vietnamensis is dominated by sesquiterpenes and diterpenes. The major components are hedycaryol (1.4–34.4%), phyllocladene (0.9–37.8%), sandaracopimara-8(14),15-diene (0.7–8.9%), germacrene D (3.7–7.9%), and α-pinene (0.8–14.9%). The oil of Xanthocyparis nootkatensis (Chamaecyparis nootkatensis) is dominated by monoterpenes. The major constituents of X. nootkatensis are limonene (35.4–42.4%), δ-3-carene (11.5–23.4%), α-pinene (8.7–16.3%) and nezukol (3.3–4.8%). The oils differ in many components but share many of the unusual diterpenes. This seems to indicate a rather distant relationship and a long period of divergence. The oil samples of X. vietnamensis were extremely variable (e.g. hedycaryol 1.4–34.4%; phyllocladene 0.9–37.8%) suggesting chemical races or botanical varieties may be present. Key Word Index: Xanthocyparis vietnamensis, Xanthocyparis nootkatensis, Chamaecyparis nootkatensis, essential oil composition, hedycaryol, phyllocladene, α-pinene, δ-3-carene, limonene.
Introduction
In 2002, a new conifer genus, Xanthocyparis, was described from northern Vietnam. The new Vietnamese species, Xanthocyparis vietnamensis Farjon et Hiep, is restricted to a small area of karst limestone in the northern part of Hagiang Province (1). The morphological features of this new conifer strongly suggested affinity to Chamaecyparis nootkatensis (D. Don) Spach in the Cupressaceae, leading Farjon et al. (1) to move Chamaecyparis nootkatensis (D. Don) Spach to the new genus as Xanthocyparis nootkatensis (D. Don) Farjon & Harder. Chamaecyparis nootkatensis has had a troubled taxonomic history having been placed in four different genera: Cupressus, Chamaecyparis, Callitropsis and Xanthocyparis (see Little et al. (2) for a review of the taxonomic history).
Recently, Little et al. (2), using ITS (nrDNA), matK and rbcL sequence data showed that Xanthocyparis is a distinct clade (Figure 1, 93% bootstrap) but the Xanthocyparis clade is closely related to the clade of Cupressus species from the western hemisphere (Figure 1, 92% bootstrap). Notice that a larger clade exists that contains Cupressus from both the eastern hemisphere (EH) and western hemisphere (WH), along with Juniperus and Xanthocyparis nested between the Cupressus (EH, WH) clades. Due to nomenclatural priority, Little et al. (2) resurrected the genus Callitropsis with two species: Callitropsis nootkatensis (D. Don) Orest. and C. vietnamensis (Farjon et Hiep) D.P. Little.
There are no analyses of the leaf oil of Xanthocyparis vietnamensis. The most recent complete analysis of the leaf oil of Ch. nootkatensis was by Cheng and von Rudloff in 1970 (3). Subsequently, totarol (trans-) was isolated from Ch. nootkatensis (4). Cool (5) found new ent-daucane and acoranes from x Cupressocyparis leylandii, but the compounds were not found in either of the putative parents (Ch. nootkatensis, Cup. macrocarpa).
In this work, we make the first report on the composition of the leaf oil of X. vietnamensis and compare it with detailed analyses of X. nootkatensis (Ch. nootkatensis) leaf oils.
